Method and apparatus for manufacturing thoriated filament devices



0d 13, 1936- R. R. HOFIL'MANI 2,057,098

METHOD AND APPARATUS FOR MANUFACTURING THORIATED FILAMENT DEVICES Filed Jan. 4, 1936 ATTO R N EY Patented Oct. 13, 1936 UNITED STATES PATENT OFFICE METHOD AND APPARATUS FOR MANUFAC- TUBING THORIATED FILAMENT DEVICES Application January 4, 1936, Serial No. 57,474

6 Claims.

This invention relates to incandescent filament devices and more particularly to processes of carbonizing electrodes for such devices.

In certain devices for example those employing electron emitters of the thoriated tungsten type, it has been the practice to subject the electrode containing thon'a, to a carbonizing process so that an appreciable quantity of the thoria may be reduced subsequently to thorium. Inasmuch 10 as so-called thoriated tungsten cathodes depend for their emitting properties on what is believed to be a layer of thorium of atomic thickness proportions, it is very difiicult with ordinary methods of processing to produce cathodes in large quantities with a high degree of uniformity as regards emission characteristics. Because of this condition it has not been found practicable heretofore to effect the carbonization of thoriated tungsten cathodes on the usual automatic exhaust and sealing machine.

' I have found that by accurately and automatically controlling the pressure of the carbonizing gas, as well as the cathode temperature during the carbonizing and by accurately controlling the duration of the carbonizing process, it is possible to carbonize thoriated tungsten filaments or cathodes on the usual automatic exhaust and sealing machines. As a result it is possible to produce great quantities of thoriated tungsten devices such as radio tubes, with a very high degree of uniformity as between the various tubes.

An object of the present invention is to provide an improved method of processing a thoriated tungsten cathode device.

Another object is to provide an automatic mechanism for controlling with a high degree of accuracy the various factors encountered in the carbonization of thoriated tungsten electrodes and the like.

V A feature of the invention relates to a mechanism which automatically and accurately controls the pressure of the carbonizing gas in the tube or other device to be carbonized.

Another feature relates to an improved form of lamp or tube exhaust and sealing machine having means to effect the carbonization of one or more electrodes during the operation of the machine.

A further feature relates to an improved automatic valve controlling arrangement for lamp or tube exhaust machines for filling the lamp or tube with gas at a predetermined pressure.

A further feature relates to the novel organization, arrangement and relative location of parts 55 which go to make up an improved machine for exhausting, carbonizing and sealing devices having one or more thoriated tungsten electrodes. 7 7

Other features and advantages-not specifically enumerated will be apparent after a consideration of the following detailed descriptions and the 5 appended claims.

While the invention will be described herein as embodied in one well-known type of exhaust and sealing machine it will be understood that it is equally well applicable to other forms of auto 10 matic exhaust and sealing machines. Furthermore inasmuch as automatic exhaust and sealing machines for lamps, radio tubes and the like are quite well-known in the art the drawing is intended to be merely diagrammatic as to details 15 of structure of the machine as a whole. Accord-' ingly, in the drawing,

Fig. 1 is a schematic diagram of certain parts of any Well-known form of automatic exhaust and sealing machine. 20

Fig. 2 is a detailed schematic diagram of certain parts of the machine of Fig. 1.

Referring to Fig. 1, there is schematically illustrated an automatic exhaust and sealing machine such for example as illustrated in detail in Patent 996,936. In general, the machine includes a rotatable spider carrying a series of arouate hollow sectors l, 2 and 3 each sector being provided with a plurality of ports 4 to receive the lamps or tubes to be processed. The spider is 30 rotated in a step-by-step manner in the direction of the arrow by any suitable mechanism,'for example by the Geneva gear 5, which is operated from the main driving motor 6 it being understood that the Geneva movement has the same 35 number of teeth as the number of ports 4. Each of the ports 4 is connected by suitable piping to the central rotary valve designated generally by the numeral 1 the rotary valve being provided in the well-known manner with a series of ports 40 equal in number to the ports 4 so that as each lamp or tube is advanced to successive positions the particular processing for that. position is ef-' fected. In the particular machine illustrated the lamps are indexed to twenty-four successive posi- 5 tions which are indicated in the drawing by the numerals l to 24 inclusive. In positions [,2 and 3 the ports 4 are closed so that the tubes may be load-ed into the machine. In positions 4 to ID inclusive the ports are connected through the'rotary valve 1 with the first exhaust pump. In position 5 the tube is tested for leaks by any wellknown mechanism. From positions 6 to Hi there is provided a suitable oven for baking out the glass and other parts of the tube. In positions s5 l2 to 23 inclusive the tubes are connected to the final exhaust pump and while passing from positions |2 to 23 various operations are performed. Thus in positions l2 and I3 the filament is degassified by being raised to a high temperature. In position M the filament is unlighted thus allowing the tube to cool somewhat before it reaches position I5. In position l5 the automatic control mechanism illustrating schematically in Fig. 2

operates to admit the carbonizing gas at a pre- Port 1 Closed-tube loading 2 C sed 5 Leak detector 6 Manifold 7 Manifold 8 Manifold 9 Manifold 10 Manifold ll Manifold 12 Single pump 13 Single pump 14 Single pump 15 Single pump 16 Single pump Exhaust pu p lfosition in oven 17 Single pump Bombarding coil Lighting 18 Single pump' positions 19 Single pump Bombarding coil I 20 Slngle pump 21 Single pump Bomber-ding coil 22 Single pump 23 Single pump Getter flash coil 24 Glosedtipping-ofi Referring to Fig. 2 a detailed description will now be given of the apparatus which comes into operation when the tube reaches position i5. As shown in Fig. 2 port No. 15 of the rotary valve is connected by pipe I6 of glass or other suitable material to the exhaust pump: and also by pipe |8 to a supply of carbonizing material. Preferably the source |9 supplies substantially pure acetylene gas and the gas system is preferably so designed thatthe gas does not come in contact with any materials which will cause contamination. Interposed in the line I8 is any well-known form of pressure regulator 20 and also a constriction 2| whereby the gas is allowed to flow at a relatively slow but uniform rate. The flow of the c'arbonizing gas into the tube being processed is controlled by any well-known form of valve indicated schematically in the drawing by the numeral 22. This valve may be of the clamp type or of the needle valve type and is arranged to be electromagnetically operated by an electromagnet which is normally deenergized except when the tube reaches position |5 as will be described. The exhaust line 24 is also provided with a suitable valve 25 which may be similar to valve 22 and provided with an operating electromagnet 26 which is so arranged that the valve 25 is normally open except when the. carbonizing gas is being admitted to the tube. For the purpose of controllingthe timed operation of valves 22 and 25 order to effect the operation of the master relay 28 preferably the current from the supply conductors 29, 30 is rectified by a rectifier device 3| which may take the form of a vacuum tube rectifier, or a mercury vapor type rectifier. The heater or filament 32 of this rectifier is supplied with alternating current from the lines 29, 39 through step-down transformer the secondary of which has its electrical mid-point connected by conductor 33 to one terminal of the winding of relay 28, the anode or anodes 34 being connected to the line 39. The energizing circuit for master relay 28 is completed under control of the manometer 35 which is interposed in the line it as shown. This manometer may be of any well-known construction and in the particular embodiment shown it includes a mercury column 36 the. level of which is dependent upon the pressure in the line l6. Preferably the manometer is provided with a sealed-in contact 31 which when the pressure in line I6 reaches a predetermined value, completes the energizing circuit for master relay 28, this circuit being traceable from line 39, conduotor 38, rectifier 3|, conductor 33, winding of relay 28, conductor 39, contacts 31, 36, conductor 40 to line 29. I

From the foregoing it will be seen that the master relay is normally deenergized to maintain the contacts 4|, 42 closed, thus preparing a circuit for valve magnet 23 this circuit however being also controlled by the mercury switch 21. Switch 21 is controlled by a cam 43 which is driven at the required rate so that the cam makes one revolution for each indexing step of the machine. Likewise switch 44 is operated by a cam 45 which makes one revolution for each indexing step, the switches 21 and 44 remaining closed while each tube is in position |5. When therefore, the tube reaches position l5, a circuit is completed from line 30, conductor 46, winding of magnet 23, contacts 4|, 42 to line 29. Magnet 23being thus energized opens the valve 22 permitting the acetylene from source l9 to flow into, the tube. A parallel circuit can be traced through the normally closed manually operable switch 41 and the winding of magnet 26 causing the valve 25 to be closed. When the predetermined pressure'of acetylene has been admitted into the tube, the mercury column 36 makes contact with electrode 31 causing the operation of the master relay 28 which thereupon opens contacts 4|, 42. The operation of relay 28 causes the deenergization of magnets 23 and 26. If desired the relay 28 may be of the fastto-release but slow-to-operate type so that the acetylene may be maintained in the tube for a predetermined interval while the tube is in position 5. It will also be noted that when the acetylene has been admitted to the tubethe switch 44 completes a circuit over the conductors 48, 49 to cause the filament of the tube to be lighted. The duration of lighting of the filament is accurately timed since it is directly controlled by the indexing motion of the machine. By the foregoing arrangement it is possible therefore to admit pure acetylene at a fixed predetermined pressure and to maintain the filament at a predetermined carbonizing temperature and for a fixed predetermined interval of time. 1

When the tube which has thus been carbonized is indexed to position l6 switches 21 and 44 are subjected to the same cycle of operation and release to cause the next tube to be flashed and carbonized as above-described. The carbonized tube is advanced to the succeeding positions as schematically enumerated in the above schedule and in position 24 the exhaust tubulation is sealed-off and the tube removed from the machine. It will be understood of course, that the foregoing cycle of operations is repeated for each tube that is loaded into the machine.

Various changes and modifications may be made herein without departing from the spirit and scope of the invention.

What I claim is:

1. In an automatic exhaust machine of the character described, the combination of means to advance a bulb having an electrode to a plurality of successive positions where different operations are to be performed on said bulb, means automatically effective at one of said positions to admit a carbonizing gas into said bulb, means effective to shut off the gas supply when a predetermined pressure is reached in said bulb, and means to heat said electrode to a predetermined temperature in the presence of said gas.

2. In an automatic machine of the character described the combination of means to advance a bulb having an electrode to a plurality of successive positions where different operations are to be performed on said bulb one of said positions being a carbonizing position, a source of carbonizing gas, a normally closed valve in the line connecting said source to said carbonizing position, a vacuum pump, a normally open valve in the exhaust line from said pump, means automatically effective when said bulb reaches the carbonizing position to open the first-mentioned valve and to close the second-mentioned valve, and means effective to close the first-mentioned valve when a predetermined pressure of the carbonizing gas is in the bulb.

3. In an automatic exhaust machine of the character described, the combination of a platform to carry a bulb having an electrode, means to index said platform in a step-by-step motion to a plurality of successive positions, means effective in at least one of said positions to subject the bulb to a preliminary exhaust, means effective in at least one other position to subject the bulb to a final exhaust, and means effective in an intermediate position to admit a carbonizing gas into the bulb and automatically effective in said intermediate position to shut ofi the supply of carbonizing gas when a predetermined pressure is in the bulb.

4. In an automatic machine of the character described the combination of a platform to receive a'bulb to be exhausted, means to index said platform to a plurality of successive positions one of said positions being a carbonizing position, a source of carbonizing gas, a valve in the supply line from said source, an exhaust pump, a valve in the exhaust line from said pump, a master relay, a pair of switches operated when said bulb reaches said carbonizing position one of said switches arranged to close an electrical heating circuit for an electrode in said bulb, the other of said switches arranged to complete a circuit including contacts of said master relay, a pressurecontrolled relay controlling the first-mentioned valve and responsive to a predetermined pressure of carbonizing gas in the bulb to operate said master relay.

5. In combination a bulb having an electrode to be carbonized, a source of carbonizing gas, a line connecting said source tosaid bulb, an exhaust line through which said bulb can be exhausted, a valve in each of said lines, an electromagnet for controlling each valve, a master relay having at least one normally closed contact, an automatic switch effective when operated to close a circuit through the gas-control valve to open the same and to close a circuit through the exhaust control valve to close the same, both of said circuits being controlled by the said contact of said master relay, a pressure-controlled relay, and a circuit for said master relay controlled by said pressure-controlled relay.

6. In combination a bulb having an electrode to be carbonized, a gas-control valve, an exhaustcontrol valve, means for normally maintaining the gas-control valve closed and exhaust-control normally valve open, a master relay controlling both of said valves, a pair of automatic switches one of said switches when operated causing the opening of the gas-control valve and the closing of the exhaust-control valve the other of said switches completing a heating circuit for said electrode, and a pressure-controlled relay responsive to the attainment of a predetermined pressure of carbonizing gas in the bulb to cause the closing of said gas-control valve-and the opening of said exhaust-control valve.

RAYMOND R. HOFFMAN. 

